You may have seen Bill Dan at and around Crissy Field performing his improvisational art, balanced rock sculpture. File this under the "How does he do this?" department. I found this site in a round about way via a link on BoingBoing.
This site is dedicated in specific to the work of San Francisco, California balanced rock sculptor Bill Dan and to the art, discipline and craft of rock balancing in general. It includes images of Bill's balanced stones and rocks, links to other rock balancers and examples of their work, with information about naturally balancing rocks and world-wide stone balancing and rock stacking traditions.